As is well known, worn or defective bearings are replaced in order to maximize machinery performance and to prevent damage to both the machine in which the bearing is installed as well as to the system in which the machine is a component. The replacement operation for most bearings is a straight forward procedure. Even if the bearing being replaced is used in an assembly line operation, replacement will generally occur during times when the assembly line is inoperative, i.e. during scheduled maintenance periods. Unfortunately, bearings do not always last for their predicted life and may require immediate replacement.
It is also known that as bearing size increases, generally the complexity of replacement and the time necessary for replacement also increases. For large dimensioned bearings significant periods of time are necessary for replacement. As can be appreciated, a large dimensioned bearing failure requiring immediate replacement is highly production sensitive, i.e. extreme economic loss results from the bearing failure. In such situations economic loss not only includes the cost associated with bearing replacement, i.e. the purchase price of the replacement bearing, but also, takes into account the cost associated with disassembly and reassembly of the machine in which the bearing is installed as well as lost production costs while the machine is out of use. Large dimensioned bearings are typically installed in relatively large machines. It will be appreciated that such large machinery is very difficult and costly to disassemble in order to remove a failed bearing.
Slewing ring bearings are one example of a production sensitive bearing. These bearings are generally large dimensioned bearings specifically designed to accommodate oscillating rotational movements under heavy axial or thrust loading. Such bearings are typically found in heavy equipment such as hydraulic excavators utilized in strip mining. Such bearings typically include an inner ring and an outer ring having rolling elements positioned there between and adapted so that the rolling elements move along raceways formed in the rings. Typically a gear arrangement is formed on the exterior surface of either the inner or outer rings.
As will be appreciated, the cost of such slewing ring bearings is significant, generally in a range from tens to hundreds of thousands of dollars depending on bearing size. Accordingly, it is typically not the case for owners of heavy equipment to maintain an inventory of such bearings. It is more likely the situation that such bearings will be ordered after the event of bearing failure. In the event of a slewing ring bearing failure, several months or even more than a year may be required in order to replace the bearing.
In other large diameter bearing applications, for example drilling equipment used for tunnel excavation, bearing replacement is also production sensitive. In certain instances, it is required to excavate an auxiliary tunnel shaft adjacent to the tunnel shaft in which the drilling equipment is located in order to re-orient the drilling equipment for removal of the failed bearing and installation of the new bearing. As will be appreciated, such repair operations are both labor intensive and highly expensive, exclusive of other expenses flowing from the cessation of work during repair operations.
In order to detect impending bearing failure easier and earlier, U.S. Pat. No. 4,906,113 - Sague, incorporated herein by reference, discloses the provision of an inspection port. Utilization of such a structure enables in situ inspection of rolling elements and raceways to detect raceway and rolling element flaws as well as other conditions which would lead to bearing failure. Such inspections provide more predictable indications of bearing life versus relying solely on unreliable analytical predictions. Unfortunately, once the bearings disclosed in U.S. Pat. No. 4,906,113 actually failed, the same replacement procedure was necessary in order to render the equipment once again operable.
The novel solution presented by the invention, involves the use of an inspection port such as that disclosed in U.S. Pat. No. 4,906,113 and the provision of dual sets of raceways in each bearing raceway cavity. In the present state of the art, during operation only one pair of raceways is formed in each cavity to withstand load while providing rotational movement. A bearing incorporating the invention, upon failure or the detection of impending bearing failure, can be replaced in situ by utilizing the inspection port to re-orient the rolling elements within the raceway cavities such that the previously unused pairs of raceways are now utilized.
The use of a removable plug in a roller bearing and the provision of dual sets of raceways are individually not new. U.S. Pat. No. 4,606,654 - Yatsu et al., discloses a cross-roller bearing which incorporates a plug in the outer ring for assembly purposes. The plug is held in place by a pin. Once installed in the machine the pin is not removable. As indicated previously, U.S. Pat. No. 4,906,113 discloses an inspection port.
The provision of dual sets of raceways in the raceway cavity of a roller bearing had previously been utilized in relation to so-called "X" roller bearings. U.S. Pat. No. 2,430,359 Messinger, discloses one of the earliest of such bearings. In such bearings, certain of the rolling elements have their axes inclined in one direction with respect to the axis of rotation of the bearing while the remaining rolling elements have their axes inclined in the opposite direction. All raceways were used concurrently. Consequently, when one raceway became defective, the whole bearing was defective.
This same "X" arrangement was proposed in subsequent U.S. Pat. Nos. 2,430,359 - Messinger and 3,361,501 - Messinger et al. It will be noted that the later of these two patents also discloses the use of an opening and a plug in the outer ring. The X-type bearings disclosed in these patents show a single row of rolling elements and again all raceways were used concurrently. Consequently, one defective raceway resulted in the entire bearing defective. An additional problem with such bearings is that it was generally impossible to remove the plug without first removing the bearing from its installation. Moreover, removal of the plug generally also resulted in a loss of warranty for the bearing.
U.S. Pat. No. 3,814,488 - Rood, discloses two rows of rolling elements where the rolling elements are oriented in a "X" orientation in each row. In addition to the problem of having a defective bearing if only one of the raceways became defective, this bearing exhibited unpredictable load distribution. A designer using such a bearing could not be certain as to how much thrust load was present on each row.
Consequently, a need still exists for a bearing which has maximum life, for which in situ repair or replacement is possible and which is not production sensitive.